Voltage graded electrical insulator



June 3, 1969 A. M. FREY ET Al- VOLTAGE GRADED ELECTRICAL INSULATOR Filed Nov. 29, 1967 l? i *44 J4 I l a I 4J l c2 l g/L/g Mmm/Vph United States Patent O 3,448,205 VOLTAGE GRADED ELECTRICAL INSULATOR Albert M. Frey and Joseph W. Griffith, Portland, Oreg., assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Nov. 29, 1967, Ser. No. 686,498 Int. 'CL H01b 17/48 U.S. Cl. 174-141 2 Claims ABSTRACT F 'IHE DISCLOSURE Summary of the invention This invention relates generally to voltage graded electrical insulators. More particularly, it relates to such insulators wherein capacitance means are incorporated in the form of enclosed spaces having electrically conductive walls to provide linear voltage grading.

lPost type and suspension type insulators are adapted to have a high potential difference existing between their opposite ends during operating. If, for example, there is unequal or nonlinear voltage division between the line and the ground end of the insulator caused by stray capacitance, there is a danger of corona discharge and flashover. Nonlinearity can be overcome if voltage divicling means such as resistors, capacitors 0r inductors are placed in circuit with the insulator. Capacitor type dividing means are most preferable because of their high frequency response spectrum.

In accordance with the present invention, there is provided an insulator having a plurality of cavities disposed along its linear axis. The interior wall surface of each cavity is coated with an electrically conductive film thereby providing a capacitor type voltage dividing means in the insulator to provide linear voltage grading therealong.

In accordance with a preferred embodiment of the invention, the insulator body comprises a plurality of modules made of insulating material which is stacked along an axis. Each module comprises a cylindrical top flange, a cylindrical Ibottom flange, an outwardly extending skirt, and an internal diaphragm. The top flange of one module cooperates with the bottom flange of another adjacent module to dene a cavity. Portions of the cavity wall which are electrically conductive, are electrically interconnected by a conductive spring.

Objects of the invention It is an object of the present invention to provide improved voltage graded electrical insulators having capacitor type voltage dividing means therein to provide linear voltage grading.

Another object is to provide such insulators which are substantially corona free, have better flashover characteristics than conventional insulators of the same length, and are lighter in weight and use less material than insulators of the same length.

Another object is to provide such insulators which are made -up of pluralities of modules, which modules are relatively easy and economical to manufacture, handleand assemble.

Another object is to provide such insulators wherein voltage grading is provided by cavities which have electrically conductive lms on the wall surfaces thereof.

Another object is to provide such insulators which combine the appearance and mechanical strength of a post type insulator with the deep undercut skirts of cap and pin type insulators.

Other objects and advantages of the invention will hereinafter appear.

Drawings The accompanying drawing illustrates a preferred embodiment of the invention :but it is to be understood that thel embodiment illustrated is susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a cross sectional view of a post type insulator in accordance with the present invention; and

FIG. 2 is a ybottom plan view of a module employed in the insulator shown in FIG. 1.

Description of the invention Referring to FIG. 1, there is shown a post type insulator in accordance with the present invention. The insulator comprises a body 10i made up of a plurality of insulator modules 12, 14, 16 and 18 which are disposed along an axis and body 10 is provided at its opposite ends with electrically conductive caps or end pieces 20 and 22 which adapt the insulator for mounting. It is to be understood that in operation, a substantial potential difference (-on the order of tens of thousands of volts) exists between the end pieces 2l)` and 22 of the insulator. In practice, the end pieces 201 and 22r are provided with suitable mounting means, such as the bolts 24, and with convolutions or recesses 26 which adapt them to interfit with the insulator modules with which they are associated.

The insulator modules 12, 14, 16 and 18 are identical to each other and therefore only module 12 will be described in detail. Each module is fabricated of suitable inorganic or organic insulating material such as ceramic, alumina, silica, alumina silicate, procelain, epoxy or polyester resin. As FIGS. 1 and 2 show, module 12 comprises a cylindrical top flange 30, a cylindrical bottom flange 32, and a heavily undercut radially disposed skirt 34, all of which are concentric with the axis of the insulator body 10. A diaphragm 36 is disposed inside module 12 and is centrally located in line with skirt 34, approximately equidistant between the ends of the module to give the optimumA voltage gradient or field plot across the module. Preferably, the outside diameter of the bottom flange 32 is less than the inside diameter yof the top flange 30 to permit nesting of modules as shown in FIG. 1. The component parts of module 12 cooperate to define a top depression 40` and a bottom depression 42.

Individual modules such as 12, 14, 16 and 18 are stacked and bonded together by a suitable adhesive provided at the joints 44 to provide a complete insulator body 10. Insulator body 10` has the appearance and rigidity of a post type insulator but has the deep undercut skirts of a conventional cap and pin type insulator. It should be noted, however, that designs of each module such as 12, are so good from an electrical standpoint that the adhesive at the joints 44 is required only for mechanical and not electrical purposes. Accidental puncture of an insulator module would not reduce overall electrical strength.

Nonuniform voltage gradient characteristics which would otherwise inhere in the insulator are overcome by providing means for capacitance grading in insulator Ibody 10. Specifically in module 12, the diaphragm 36 is used as a dielectric medium between two capacitor members, plates or lrns 46 and 48 which take the form of electrically conductive metal, such as zinc, sprayed or otherwise deposited on the diaphragm surfaces. In practice diaphragm '36 should be kept as thin as possible to provide maximum capacitance. The lms 46 and 48 extend beyond the di-aphragm. surfaces and out the walls of the depressions 40 and 42 to provide a shielding effect and to relieve the walls of module 12 from high voltage gradients.

A-n electrically conductive element such as the coil springs 50 are placed between adjacent modules during assembly to assure electrical Contact between adjacent modules.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrical insulator comprising,

a plurality of stacked modules made of insulating material,

each module comprising a top llange defining an upper depression, a bottom ange dening a lower depression, a diaphragm separating said depressions and a radial skirt on the exterior of said module, said bottom. 'flange being shorter and having a smaller outside diameter than said top ange whereby when two or more modules are nested the underside of said skirt of the upper module rests on the top ange of the adjacent lower module and the top flanges of all modulesare in alignment and the lower depression of the upper module cooperates with the upper depression of the lower module to dene a cavity,

adhesive material between the inner and outer surfaces of the top and .bottom ilanges, respectively, for joining adjacent modules,

rst and second electrically conductive coatings on the surfaces of the upper and lower depressions, respectively, of each module,

and electrically conductive spring means in each cavity for electrically connecting the .first and second electrically conductive coatings therein.

2. An insulator according to claim 1 comprising a rst electrically conductive end cap which cooperates with the top ilange of the uppermost iof said modules to define an uppermost cavity,

a second electrically conductive end cap which cooperates with the 'bottom flange of the lowermost of said modules,

said first and second end caps being adapted for mechanically and electrically connecting said insulator in a circuit,

electrically conductive spring means in said uppermost ycavity for electrically connecting said rst end cap and the electrically conductive coating in said cavity,

and means for electrically connecting said second end cap and the electrically conductive coating on the surface of the lower depression of said lowermost module.

References Cited UNITED STATES PATENTS 1/ 1912 Hilliard et al 174-179 X 10/1917 Lincoln 174-141 7/ 1930 Dunmire 174-179 X 5/1967 Frey 174-30 X U.S. Cl. X.R. 

